Four pole transducer



July 5, 1960 J. A. ROSS FOUR POLE TRANSDUCER 2 Sheets-Sheet 1 Filed July 18, 1958 FIGfl.

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FIG. 3.

INVENTOR.

JAMES A. ROSS BY ii fiw AGENT July 5, 1960 J. A. ROSS FOUR POLE TRANSDUCER 2 Sheets-Sheet 2 Filed July 18, 1958 FIG. 4.

FIG. 5.

FIG. 6.

INVENTOR.

JAMES A. ROSS BY zk wmb AGENT United States Patent FOUR POLE TRANSDUCER James A. Ross, San Fernando, Calif., assignorto Ling- Altec Electronics, Inc., Dallas, Tex., a corporation of Delaware Filed July 18, 1958, Ser. No. 749,539 18 Claims. (Cl. 317-423) My invention relates to an electrical to mechanical transducer and particularly to such a transducer having a unitarycross-shaped armature with a field structure to pass magnetic flux through each arm of said cross-shaped armature.

For decades electromechanical transducers have been constructed with a circular armature coil. A magnetic field structure has been arranged external and internal thereto to provide magnetic flux across an annular airgap occupied by the armature coil.

This configuration has certain shortcomings, which have been accepted as inevitable. The flux density at the air gap has been limited by the saturation of the iron of the field structure adjacent thereto and the proportions of that structure could not be modified to alleviate this condition. a

A mechanical bridge has always been required to attach the armature coil to a useful load. This bridge has taken the form of a diaphragm for sound reproduction or a shake table for vibration testing. It has always added mass. and has complicated the inherent vibrational characteristic of the movable system.

Because the cross-section of prior art field structures have been far from uniform, the flux density has been low in the major portion of that structure. As a consequence, prior transducers have usually weighed about twice what would otherwise be require I have been able to overcome these shortcomings of the prior art and to also attain additional advantages by departing entirely from the structures of the past.

Rather than a multiturn coil of circular shape I employ a bar of solid metal for an armature, having a crosssection in the form of a cross with arms of equal length and thickness. For increased power-handling capability this bar is merely lengthened. I

Rectangular pole pieces front each side of each arm of the cross. A return field path of essentially uniform cross-section is accomplished by the lobate shape to be noted in the drawings. Windings for producing a'magnetomotive force therein form magnetic poles of opposite sign on opposite sides of each arm of the cross.

In an initial embodiment flexible connections to the extremity of each arm of the cross and two co-phased current sources of actuating current cause this current to flow in one arm and out of an adjacent arm for each of the two pairs of arms. A laminated shading coil is wound upon two adjacent stationary pole faces and another one diagonally opposite to reduce the inductance of the armature system. Each pair of shading coils are externally connected back on itself to give a closed circuit.

The armature is positioned laterally by fluid pressure exerted between the arms of the cross and adjacent pole faces according to a symmetrical diagonally opposed pattern. It is positioned longitudinally by a restoring spring member at one end of the armature. The useful mechanical load is directly attached to the opposite end of the armature.

I In an'alternate embodiment the exciting voltage from 2,944,194 Patented July 5 1960 2 a generator or amplifier is connected tothe shading coil conductors which are connected in series within the coil. This allows optimum impedance match for eflicient power transfer. The actuating current is inductively coupled to the moving armature conductive arms.

In a second alternate embodiment longitudinally separate current inputs are provided at the armature, phased in time to correspond to the sonic characteristic of the armature. This arrangement theoretically removes the upper frequency limit of vibration of the armature.

An object of my invention is to provide a simple and novel armature for an electromechanical transducer, which armatureis one solid conducting piece.

Another object is to provide a lobate field structure surrounding said armature for providing magnetic flux therethrough.

Another object is to minimize inherent resonant fre-' quencies in the armature of an electromechanical trans ducer.

Another object is to employ shading coils as a means of impedance transformation in driving an electromechanical transducer.

Another object is to reduce the mass of the armature system of an electromechanical transducer.

Another object is to provide novel means to resiliently support the armature of an electromechanical transducer.

Another object is to provide a rugged armature member.

Another object is to provide an armature member which may be fed with a sonic signal in phase with the sonic characteristic of that member, thereby to remove the theoretical upper frequency limit to its vibration.

Another object is to provide an electromechanical transducer structure which may be electrically connected in a number of ways.

Another object is to provide an electromechanical transducer structure which is relatively simple, easy to manufacture, relatively light weight and relatively inexpensive.

Other objects will become apparent upon reading the following detailed specification and upon examining the accompanying drawings in which are set forth by Way of illustration and example certain embodiments of my invention.

Fig. 1 shows a perspective view of the essential structure of my transducer,

Fig. 2 shows a sectional view of the coactive stationary and movable portions of that structure,

Fig. 3 is a schematic representation of external circuit connections arranged to drive the armature directly,

Fig. 4 is a schematic representation of external circuit connections arranged to drive the armature inductively from the shading coils,

Fig. 5 shows a sectional view of an alternate embodiment of my invention in which multiple circuit connections are provided for feeding the electrical input to the armature in correspondence with the sonic phase thereof, and

Fig. 6 shows the schematic circuit diagram for driving this type of transducer. i

In Fig. l numeral 1 indicates the iron field structure. The cross-section of the flux paths are essentially uniform throughout. The armature 2 fits in the central cross-shaped aperture in the field structure. Field coils' 3, 4, 5, 6 are connected in opposite phase directions on opposite sides of the field structure so that like magnetic poles are produced diagonally opposite. This gives a strong magnetic field through each arm of the cross. In

a typical embodiment capable of handling ten kilowatts" of signal power applied to the armature, the field wind-' serially a magnetic flux density of ninety thousand lines" per square inch is produced. It will be noted that with my configuration the path cross-section is substantially uniform through the coils, at the working gap and through the iron connecting the two.

Facing four diagonally related pole faces and continuous as a single conductor along a pair of adjacent pole faces are the conductors of the laminated shading coil 7, 8. These are individually insulated copper bars which lie one above the other in tiers along adjacent pole faces. Numerals 7 and 8 identify the top conductor of one shading coil as lying along two adjacent pole faces. The second shading coil is diagonally opposite on the two faces comprising the other N pole. Only the portion 7' can be seen in Fig. 1 because of the perspective nature of the figure.

In the first embodiment the signal energy is fed to the extremity of the armature cross arms. This is accompli'shed by a number of flexible connections between a stationary bus and the extremity of each arm. The upper ends of these buses are seen in Fig. lat 9, 10, 11, 12. The upper flexible connection is also seen on two of the buses, at 13 and 14. On the other buses the perspective view is such as to somewhat obscure these connections in Fig. 1, but these may be seen in other views.

* In Fig. 1, several holes 15 are shown in the top of the armature 2. These are normally threaded and are employed to mount the specimen to be vibrated directly to the armature, as has been mentioned.

In Fig. 2 a vertical section of the transducer shows the armature 2 supported by springs at the bottom thereof,

at 17. These are flat leaf springs of the same general nature as those employed in supporting the body over the rear axle in an automobile, and are shown here in section. These springs, in turn, are supported by general base 18. The field structure 1 and the field coil 3 are shown at the right in Fig. 2. The section line for this half of the figure is in the gap in front of the armature arm 2, as is also indicated by the dashed line in Fig. 1, Stationary bus 9 is also shown, with several flexible connections 19, 20, 21, 22, 23. The current carried decreases from. bottom to top on this bus, thus it is narrower at the top.

On the left hand side of Fig. 2 the section has been taken just to there'ar of the armature cross, so that this ele'ment'is' absent and the laminated shading coil can be seen. The separate conductors 25', 26, 27, 28, 29, 30, 31, 32'a're separately insulated from each other and from the, field structure. These are relatively heavy bars of a good conductive material such as pure copper or perhaps, aluminum. Silver would be desirable from the conductivity standpoint for both armature and shading coils, but the cost is excessive because of the amount. Silver plating is not effective in increasing the. conduction through the whole volume of the conductor and the whole volume is" involved in conduction at the audio frequencies at which my transducer operates. Howevensilver plating may be employed to reduce contact resistance, as for crimped ype circuit connections. Welded connections and low resistance soldered connections represent good techniques, also. The resistance of the armature and shading coil circuits must beheld to an absolute minimum in view of the low impedance of these circuits, this being a small fraction of an ohm.

The conductors of the shading coils may be connected in series or in parallel. The latter connection can be accomplished by electrically connecting all conductors at each end of a shading coil entity, as 7, 8 in Fig. 1, together with a copper strap. These straps. are interconnected according to Fig. 3, to be described later.

When the series. connection is.desired, one external lead is provided for eachconductor of the shading coil. These eachhave a cross-section commensurate with the crossseotion of the shading coil conductor, as 25, 26, etc., and are showngrouped at 3-4 in Fig. 2. The external leads atccxternally connected so that one end of conductor 25 is. connected-to the opposite end of conductor 26, etc.

This makes all the conductors 25, 26, etc. in the working magnetic field carry a current in the same direction and thus be effective as a coil of several turns. The first end of the first turn, 25, and the last end of the last turn, 32, constitute the external connections. of one shading coil, to be later described in considering Fig. 3.

The bottom springs 17 support the armature vertically, but an additional medium is required to accurately position the armature laterally with respect to the pole pieces and the shading coils. This medium is high pressure oil. An oil circulating system is employed consisting of an oil pump and/ or reservoir, a gear type proportional oil flow divider and pipes to convey the metered amount to each of four pole faces in a symmetrical diagonally opposite pattern. The oil pump should be capable of maintaining a pressure of the order of 2000 pounds per square inch. The flow divider divides the output of this pump into four equal amounts of oil so that the forces exerted on each of the cross arms will be the same.

In Fig. 1 suitable pole faces for dispensing the oil are the diagonally opposite S ones, which do not have the shading coils. On each face the oil inlet from one of the four pipes previously mentioned is located at the center and a spiral groove progresses outwardly to near theouter limits of the face. The clearance between the shading coils and the armature is of the order of a few thousandths of an inch, also the same between the pole faces not having shading coils and the armature. The equalized oil pressure holds the armature centered in the cavity thus provided. The oil flow is effective in cooling the armature and the shading coils under heavy signal loads. A thin transformer oil having an S.A.E. equivalent of five is suitable, one example of which is the Shell Dyala oil.

If, without shorting the shading coils, a spiral oil groove is formed in them the faces of the diagonally opposite N poles may be used to handle the oil pressure, either instead or in addition to the use of thesouth poles previously mentioned. V T

The electrical impedance of the output of, thegtypical high power amplifier suited to operate my transducer is in the range of at least hundreds of ohms. The impedance of my armature at an average audio frequency of 400 cycles is 0.005 ohm. Accordingly, an impedance transformation system having large step-down ratio is required.

The basic element of this system. is transformer 35, shown in Fig. 3. Primary 36 is normally connected to the low impedance secondary of the usual power amplifier output transformer, the impedance of which is. a few ohms. An output transformer is not shownin Fig. 3, since it is standard; however, such a transformer is similar to transformer shown in Fig. 4.

In Fig. 3 two essentially one turn secondaries 37 are paralleled and connected to two adjacent extremities of the cross of armatureZ. Two more paralleled secondaries 38 of the same characteristics connect to theother two extremities of the cross. Because these secondary circuits are of such extremely low impedance, transformer 35 is located directly at the transducer 1, 2. The connecting leads are of large cross-section and are as short as possible. Also, more than two secondaries maybe paralleled in each connection.

In order that the shading coils may act in reducing the armature inductance each is connected back on itselfto provide a continuous path for current flow. Thus, one shading coil terminal 44 is externally connected tothe opposite terminal 45 of the same shading coil. This. COD-r ductor is run closely parallel to the leads from: secondary 37 to the adjacent armature terminals to keep the inductance of the armature circuit at a minimum, Shading coil' terminals 46 and 47 are also connected together. in a similar manner.

In the alternate embodiment of Fig. 4 I' amableto eliminate transformer 35 by feeding theinput signal for the transducerto the shading coils connected inseries rather than to the armature per se. The armature is then excited inductively from the current flowing in the shading coils. The coeflicient of coupling between the two circuits is high, approaching unity, so that the efiiciency is high and the leakage reactance small.

In Fig. 4, transformer '40 is the output transformer for the power amplifier driving stage. This stage is partially indicated for completeness. It is connected to primary 41. Identical secondaries 42 and 43 each have an impedance of one-tenth or less that of primary 41. Secondary 42 connects to terminals 44 and 45 of one shading coil and secondary 43 connects to terminals 46 and 47 of the other shading coil. Both secondaries are connected to give the same alternating current phase. The conductors of these shading coils are connected in series for this embodiment, in the way that has been previously explained.

In this embodiment the extremities of the armature cross are connected back on themselves with conductors which move with the armature. These are out of the magnetic field and are shown as conductors 48 and 49 in Fig. 4. These are copper bar (or equivalent) conductors located either or both above and below. the field structure. In this embodiment the stationary bus 9 and flexible conductors 1923 of Fig. 2 are not required.

Without limiting my invention it may be noted that the dimensions for a representative embodiment capable of handling an audio frequency vibratory signal of 50 kilowatts may be 30" across the extremities of the arms of the cross armature by a depth perpendicular to this dimension of 20".

We now consider the and 6.

The velocity of propagation of sound in a metal such as aluminum of which the armature may be made is relatively high. A convenient depth for my armature, such as 20", corresponds to a quarter-wavelength of the audio frequency of 3,000 cycles. A quarter-wavelength is the distance between a node and a loop of vibratory wave energy. It is seen that the electrical driving energy and the vibratory response of the armature thus sufier important phase displacement along the depth of the armature. This results in decreased efliciency in transducers of the large size required in vibration practice.

In my transducer it is possible to segmentize the armature vertically and to feed each segment separately with signal energy phased to drive that segment in phase with the phase of the vibration of the armature at that position.

The altered armature construction necessary to accomplish this is shown in Fig. 5. The armature 2 may now be considered restricted to a top shallow section, while successively lower sections 50, 51, 52, 53, 54 are all of equal depth and are insulated one from the other. This structure may consist of insulated dovetail joints between each section according to the construction of the known commutator of rotating electrical machinery. Specifically, the dovetails run down the center of each arm of the cross with mica insulation completely separating all surfaces of the joint. This. is shown at 60, 61, 62, 63 in Fig. 5.

In connecting the first embodiment of the segmented armature to external circuits the same general mechanical arrangement formerly employed at 9 in Fig. l is followed. However, each flexible lead is insulated from all others and connects to only one section In Fig. combined insulated bus and flexible connection 55 feeds the top section 50 of'the armature, another insulated bus and flexible connection 56 feeds section 51, and so on, through combination 59 feeding section 54. It will be noted in Fig. 5 that the shading coils, the magnetic structure and the supporting structure are unchanged from Figs. 1 and 2.

Fig. 6 shows how this type of transducer is externally further alternate of Figs. 5

reproducing heads.

connected. i A series of transformers 90' is previded;

equal in number to the number of sections of the armature. This is five in the present example; The several primaries are fed with input signal of successively delayed phase in equal increments. The phase of the signal energy in primary 66 is delivered to the lowest armature section 54 and may be considered zero or reference phase. The phase of the signal energy in primary 67 is delayed an amount of time equal to the sonic time delay between sections of the armature structure. In the example given this would be one-fifth of 'ninety electrical degrees, or 18 electrical degrees at 3,000 cycles. This is a time of 17 microseconds. The time delay is provided by separate power amplifiers for each of the primaries 66-70 and a delay line at the input to each amplifier. As an alternate to delay lines a magnetic tape loop with one recording head and four evenly spaced A separateamplifier for each re producing head and for .the undelayed signal as well is provided. These elements are known and so are not illustrated.

It is desirable to terminate the armature in a mechanical impedance that is resistive at all frequencies where the depth dimension of the armature becomes an appreciable fraction of a wavelength; i.e., as above 1,000 cycles. This is accomplished by means of dashpot 64 fastened to stationary frame 18 and having plunger 65 fastened to armature 2. Oil, or an equivalent liquid, in the pot provides the damping medium.

Returning to Fig. 6, the transformer of primary 66 has two substantially one-turn secondaries 71 and 72. The two terminals of secondary 71 are connected to two terminals generically represented as 81 and 82. These terminals represent all the separately insulated connection which connect to the sectionalized armature cross. Accordingly, the upper connection of secondary 71 connects to the bus-flexible connection 59 of Fig. 5 and the lower connection of this secondary to a companion connection which is not shown in Fig. 5 but which connects to the extremity of the arm shown in section of the same segment 54 of that figure. I

In the same manner, secondary 72 connects to the bottom armature section 54 on the opposite diagonal of the cross, this being generically represented by terminals 83 and 84 in Fig. 6. The same sequence of connections occur for each of the several primaries 66 through 70 and secondaries 71 through 80.

In this embodiment the shading coils are connected externally back upon themselves. These are connections 85 and 86 in Fig. 6 and directly connect the opposite ends of shading coils on adjacent sides of a given magnetic pole. g

A second important embodiment of the segmented armature transducer consists in feeding the signal to sectionalized shading coils and connecting the armature cross extremities together, as was done in a non-sectionalized manner in Fig. 4. With this arrangement the impedance transformation required is reduced, as before. The time phasing is obtained as above because both the armature and the shading coils are sectionalized.

In these ways I provide several related embodiments of a novel transducer, or shaker. It will be noted that the embodiment of Fig. 4 is unusual in that no flexible connections are required between stationary and movable elements and that the same is true of the allsectionalized embodiment just described.

Certain further alternate embodiments are possible.

A permanent magnet field structure may be used instead of the electromagnet structure shown.

Transformer 35 of Fig. 3 may be replaced by two transformers each having one primary and one secondary. Transformer 40 may be similarly replaced, although this is not usual if it connects to an output amplifier stage.

Other physical modifications may be made in the combinations, arrangement, size, proportions or shape of my device. It will be understood, that it is suitable for miniaturized applications as well as the high power embodiments described. Other modifications in the character of the circuit elements, details-of circuit connections and alteration of the coactive relation between the elements may also bernade without departing from the scope of my invention Having thus fully described my invention and the manner in which it is to be. practiced, I claim:

1. A transducer comprising an armature of cross crosssection, laterally disposed means to impress a magnetic field through the arms, of the armature cross, conductive means inductively related to said armature cross, means to cause a motional actuating current to fiow in said armature, and means to position said armature within said magnetic field.

2. A transducer comprising an armature of cross crosssection, a magnetic field structure laterally enclosing the arms of the armature cross, conductive means upon said field structure inductively related to the arms of said armature cross, means to vibrate said armature by causing an actuating current to flow in it', means to resiliently position said armature within said field structure for the vibratory motion of said armature, and means to attach a load directly to an end of said armature.

3. An electromechanical transducer comprising an armature of cross shaped cross-section, a magnetic field structure having pole faces substantially abutting each side of the armature cross, shading coils having insulated conductors located upon said pole faces, external conductors connected to said armature cross, external conductors connected to said shading coils, means to actuate said armature by passing actuating current through at least some of said external conductors, means to laterally position said armature within said field structure for the free motion of said armature parallel to the surfaces of said pole faces, restoring means to longitudinally position said armature, and means to attach a load to said armature located at one end thereof.

4. An electrical to mechanical transducer comprising an electrically conductive cross-shaped armature of symmetrical cross section, a laterally disposed stationary magnetic field structure having pole faces substantially abutting each side of the armature cross, two shading coils having insulated conductors located symmetrically upon diagonally opposite pole faces, external conductors connected to the extremities of the four arms of said armature cross, external conductors connected to said shading coils, means to vibrationally excite said armature by passing actuating current through said external conductors, liquid pressure means to laterally position said armature within said field structure for the free motion of said armature, restoring means to longitudinally position said armature located at one end of said armature, and means to directly attach a mechanical load to said armature located at the other end thereof.

5. An electromechanical transducer comprising an armature of cross cross-section, means to impress a mag netic field transversely of each arm of said cross, and means to pass an actuatingcurrent through adjacent arms of said cross for the motional excitation of said armature 6. An electromechanical transducer comprising a conductive armature of cross cross-section, field poles facing and substantially coextensive with each side of the armature cross, means to form magnetic poles of opposite polarity on each side of said armature cross, a closed circuit shading coil upon diagonally opposite said pole faces, electrical means to convey an actuating current in one arm and out an adjacent arm of said armature cross, means to longitudinally and laterally resiliently support said armature, andmeans to attach a mechanical load directly tov an end of said armature.

7, An electromechanical' transducer comprising an electrically conductive. cross-shaped armature of symmetrical cross-section, a stationary permanent magnetic field structure, said field structure having pole faces substantially abutting each side of the armature cross, two shading coils having insulated conductors located upon diagonally opposite pole faces, flexible conductors connected to each extremity of the four arms of said armature, transformer means having tWolow impedance secondaries, one said secondary connected to the flexible conductors of two adjacent extremities of said four arms and the other said secondary similarly connected to said means at the other two adjacent extremities, liquid pressure means to position said armature within said field structure for the free motion of said armature, restoring means located at one end of said armature and means to attach a load located at the other end of said armature,

An electrical to mechanical transducer comprising a solid electrically conductive armature of cross-shaped cross-section, said armature having four arms of substantially equal length and equal thickness, a stationary ferromagnetic hollow lobate field structure, said field structure having pole faces substantially abutting, each side of the armature cross and having windings in the hollows of said lobate structure to form magnetic poles of opposite sign on each side of said armature cross in response to unidirectional electrical current in said windings, a shading coil having separately insulated conductors positioned upon each diagonally opposite pole face, flexible conductive means connected to each extremity of the four arms of said armature, two impedance matching transformers each having a low impedance secondary, one said secondary connected to said flexible conductive means of two adjacent extremities of said four arms and the other said secondary similarly connected to said flexible conductive means of the other two adjacent extremities, oil pressure means symmetrically disposed over half of the number of said pole faces to laterally position said armature within said field structure for the free motion of said armature in response to electric current from said secondaries, mechanical restoring means to longitudinally position said armature attached at one end of said armature and means to directly attach a mechanical load at the other end of said armature.

9. An electromechanical transducer comprising a crossshaped armature, means laterally disposed with respect to said armature to impress a magnetic field through each arm of said cross, stationary insulated conductors interposed between said means to impress a magnetic field and diagonally opposite faces of the arms of said cross, and means to pass a current through said conductors to actuate said armature by magnetic induction.

10. An electromechanical transducer comprising a conductive armature of cross shape, field pole faces adjacent to each side of the armature cross, means to form magnetic poles of opposite polarity on each side'of each arm of said armature cross, a shading coil upon at least two pairs of adjacent said pole faces, means to pass an actuating current through said shading coils, external connections between the extremities of adjacent arms of said armature cross, means to resiliently support said armature and means to attach a mechanical load directly to an end of said armature.

11. An electrical to mechanical transducer comprising an electrically conductive cross-shaped armature of symmetrical cross section, a stationary magnetic field strucire having pole faces substantially abutting only each of the eight sides of the armature cross, two shading coils having insulated conductors located symmetrically upon diagonally opposite pole faces, external conductors connected to the extremities of the four arms of said armature cross, external conductors connected to said shading coils, means to vibrationally excite said armature by impressing an actuating voltage upon the external-conductors connected to said shading coils, liquid pressure means to position said armature within said fieldstructure, armature positional restoring meansloc-ated at an end of said armature, and means to attach a load to said armature at an end thereof.

12. An electromechanical transducer comprising a solid electrically conductive cross-shaped armature having arms of substantially equal length and thickness, a stationary lobate magnetic field structure, said field structure having pole faces substantially abutting only each side of the armature cross and having windings in said lobate structure to form magnetic poles of opposite sign on each side of said armature cross in response to electric current in said windings, a shading coil having separately insulated series-connected conductors positioned upon diagonally opposite pole faces, conductive means outside of the magnetic field of said field structure connected to each extremity of the four arms of said armature, an impedance matching transformer having two low impedance secondaries, one said secondary connected to one said shading coil for the inductive actuation of said armature and the other said secondary similarly connected to the other said shading coil, fluid pressure means to position said armature within said field structure for the free motion of said armature in response to electric current from said secondaries, mechanical restoring means located at one end of said armature and means to directly attach a mechanical load at the other end of said armature.

13. An electromechanical transducer comprising a cross-shaped armature insulatingly sectionalized in a direction perpendicular to said cross shape laterally disposed means to impress a magnetic field across each arm of the cross, and means to pass an actuating current through at least one pair of adjacent arms of each of the sections of said cross, with means to delay said actuating current from section to section along said armature to match said actuating current to the vibratory phase of said armature.

14. An electromechanical transducer comprising a conductive armature of cross cross-section having plural cross-shaped sections longitudinally insulated one from the other, field pole faces adjacent to each side of the armature cross, means to form magnetic poles of opposite polarity on each side of said armature cross, shading coils upon at least one pair of diagonally opposite pole faces, said shading coils sectionalized as said armature, electrical means to convey an actuating current in at least one arm and out an adjacent arm of said armature cross, means to successively delay said current from section to section of said armature cross, means to resiliently support said armature, and means to attach a mechanical load directly to an end of said armature.

15. An electromechanical transducer comprising a longitudinally sectionalized electrically conductive crossshaped armature having arms of substantially equal length 7 and equal thickness, a stationary lobate magnetic field structure, said field structure having pole faces substantially abutting each side of the armature cross and having windings in said lobate structure to form magnetic poles of opposite sign on each side of said armature cross in response to electric current in said windings, a sectionalized shading coil having separately insulated conductors positioned upon each diagonally opposite pole face, flexible conductive means connected to each extremity of the four arms of said armature, plural impedance matching transformers each having two low impedance secondaries, one said secondary connected to the said flexible conductive means of two adjacent extremities of one section of said four arms and the other said secondary similarly connected to said flexible conductive means of the same section at the other two adjacent extremities, other said secondaries similarly connected to other said sections, means to effect a successive time delay between corresponding energization of each said section, means to position said armature within said field structure for the free motion of said armature in response to electric current from said secondaries, restoring means located at one end of said armature, and means to directly attach a load located at an end of said armature.

16. An electromechanical vibration device comprising a cross-shaped armature insulatingly sectionalized in a direction perpendicular to said cross shape, means to impress a magnetic field across each arm of said cross, said means laterally disposed with respect to said cross, shading coils symmetrically adjacent to said cross, and means to pass an actuating current through said shading coils to induce an actuating current in said armature.

17. An electromechanical transducer comprising a conductive-cross armature having plural transverse sections insulatingly longitudinally related, field pole faces adjacent to each side of the armature cross, means to form magnetic poles of opposite polarity on each side of said armature cross, a shading coil upon at least one pair of diagonally opposite pole faces sectionalized as said armature, electrical means to convey a successively delayed actuating current to said shading coils in order, means to electrically coimect together at least two adjacent arms of each section of said armature cross, means to resiliently support said armature, and means to attach a specimen load directly to an end of said armature.

18. An electromechanical transducer comprising a longitudinally sectionalized electrically conducting crossshaped armature having arms of substantially equal length and equal thickness, a stationary magnetic lobate field structure, said field structure having pole faces substantially abutting each lateral side of said armature cross and having windings in said lob ate structure to form magnetic poles of opposite sign on each side of said armature cross in response to electric current in said windings, two sectionalized shading coils having insulated conductors each positioned on diagonally opposite pole faces, external conductive means connected to each extremity of the four arms of said armature, plural impedance matching transformers each having two low impedance secondaries, one said secondary of each transformer connected to the shading coil of one section and the other said secondary of the same transformer connected to the diagonally opposite shading coil of the same section, means to successively energize said transformers to correspond to the sonic delay along said armature perpendicular to said cross shape, pressure means to position said armature Within said field structure for the free motion of said armature within said field structure in inductive response to electric current flowing successively in said shading coils, restoring means located at an end of said armature, and means to directly attach a mechanical load located at an end of said armature.

Wahl Oct. 27, 1925 Marchand Dec. 20, 1955 

